This invention relates to the non-contact repair of microcircuits and in particular to the repair of simple and active matrix liquid crystal display panels, printed circuit boards, hybrid integrated circuits, and multiple-chip modules.
Manufacture of the aforementioned devices is complicated by the high number of microcircuits on each device. For example, an active matrix liquid crystal display panel may have over 1,000,000 thin-film transistors having a process area as high as 350 cm.sup.2. This creates a formidable yield problem even for VLSI and ULSI manufacturing techniques. For example, a typical yield of shipped panels of high density active matrix LCD is only 10%. Repairing defective locations on the LCD panel can significantly increase the yield of such panels.
One system used in the repair of LCD panels is the Micrion L1 manufactured by Micrion Corporation of Massachusetts. The Micrion L1 system is capable of cutting through metal lines and depositing metal on the surface of an LCD panel. Thus, the Micrion L1 system may be used to repair a line-to-line (adjacent line) short. To repair the short, a laser is used to cut the conductive path in order to separate the traces. Although the Micrion system can repair a line-to-line short, use of the Micrion system is limited. The Micrion system cannot correct an open defect or perform a cross-short repair since it is unable to selectively remove a passivation layer. The inability to correct open defect and perform cross-short repairs limits the ability of the Micrion system to increase LCD panel yield.
Another limitation of the Micrion system is its high equipment complexity. The Micrion system uses a deposition technology based on a photolytic process. In operation, an LCD panel is placed within a vacuum chamber. Gas is introduced into the chamber and the gas is photolytically decomposed by a laser, forming metal on the workpiece surface. Sustaining this gaseous environment increases equipment complexity since the system must support a vacuum system as well as a toxic gas delivery, venting, and management system. Furthermore, the metal deposition process of the system is very slow, having a writing speed of approximately 1 micrometer per second. The equipment is therefore of limited use in high volume manufacture and repair due to its lack of throughput and the need for operator control.
Theoretically open defect, cross-short, and line-to-line short repairs of an LCD panel could be performed by moving the panel through a series of repair systems currently available. However, such processing would be extremely cumbersome and expensive. First, the protective passivation layer would be removed by a first laser. Next, the LCD panel would be manually moved to a dispensing system where a metallo-organic fluid would be applied. After the LCD panel is allowed to dry, the panel would be manually moved to a second laser system to decompose the metallo-organic material into a pure metal.
Unfortunately, current dispensing systems are inadequate for the uniform and semiautomatic deposition of highly volatile low viscosity metallo-organic fluid used in repair such as palladium acetate in a solvent base. It is very difficult to dispense a volatile material with a very low viscosity. Attempts to air brush or air spray such a material on an LCD panel results in significant drying before contact with the panel surface. Research in the field of ink deposition, painting, brushing, and even photoresist spinning, has not resulted in a successful semiautomatic method for the localized application of a controlled width and thickness of a highly volatile material. Micropen Corporation has introduced an active feedback system for dispensing fluid over a workpiece surface. However, the Micropen system is inadequate to dispense a uniform thickness of a low viscosity fluid since it uses the fluid backpressure to set the height of the dispensing nozzle. Because of the low viscosity of the metallo-organic fluid, there is insufficient backpressure for the Micropen system to function in the environment of interest herein. The Micropen system relies on the use of a highly viscous fluid.
Another problem in current dispensing systems is contact to the workpiece surface. Since surface contact of a repair system to the workpiece can result in damage to or the destruction of the workpiece, the repair system must not contact the workpiece. Therefore, some kind of hovering device is necessary. Current hovering devices are not useful. For example, a capacitance feedback hovering system would fail since the capacitance measuring device would collapse by not having a ground plate on one side.
Current repair systems are unable to significantly increase LCD panel yield since they cannot selectively remove passivation layers and therefore cannot perform open defect and cross-short repairs. Furthermore, current systems which use gas deposition to form metal line are slow and rely on highly complex manufacturing equipment.
A repair process which would rely on transferring an LCD panel through a series of repair systems would require that the user buy and maintain three different systems to perform open defect and cross-short repairs. Transfer of the LCD panel between such systems would increase the probability of breakage, loss and contamination of the workpiece. Furthermore, an adequate dispensing system does not exist for the semiautomatic dispensation of a metallo-organic fluid. There is therefore a need in the industry for semiautomatic repair of liquid crystal display panels, PC boards, multichip modules, and the like.